Genotypic diversity of Acidovorax strains isolated from activated sludge and description of Acidovorax defluvii sp nov.

Fluorescence in situ hybridization of activated sludge samples from a munic ipal wastewater treatment plant using oligonucleotide probes specific for A cidovorax demonstrated that these bacteria are highly abundant in this envi ronment. For the targeted cultivation of representatives belonging to this genus, isolates grown on agar plates after serial dilution were screened by whole-cell hybridization with specific probes. The obtained strains clustered in two phylogenetic groups as determined by 16S rRNA gene sequence analyses. The isolates of one cluster were phylogene tically and genotypically closely related to A. delafieldii. In contrast, t he strains of the other cluster were genotypically and phenotypically disti nct from the hitherto known Acidovorax species. Therefore, a new species, A cidovorax defluvii sp. nov., was proposed for these strains. The main chara cteristics of the newly defined species are as follows: Gram-negative, moti le or non-motile rods with rounded ends, often with large polyhydroxybutyra te granules. In broth cultures flocs are formed. Test for cytochrome oxidas e is positive with all strains. The majority of strains is catalase positiv e and reduces nitrate. All strains are metabolically inactive against most carbohydrates and organic acids. Fatty acid patterns are typical for the ge nus Acidovorax. The guanine-plus-cytosine content of DNAs varies between 62 and 64 mol%. The type strain of A. defluvii is BSB411(T) (DSM 12644). A new 16S rRNA-targeted oligonucleotide probe reacting by in situ hybridiza tion with all known Acidovorax species, including A. defluvii sp. nov., was designed.